Conventionally, image sensing apparatuses such as digital cameras are commercially available, each of which senses a still image sensed with an image sensing element such as a CCD using a memory card having a solid-state memory element as a recording medium.
In these image sensing apparatuses, photographing processing is executed while temporarily writing output image data from the image sensing element in a buffer memory. Then, development/compression processing is executed in which image processing and compression processing are executed, and the image data is stored in the buffer memory again. After that, processing of writing the image data on a recording medium on a detachable card is generally performed.
White balance control in photographing processing in such an image sensing apparatus is conventionally executed in accordance with the following procedure. First, unprocessed raw data (to be referred to as RAW image data hereinafter) that is captured from the image sensing element into the memory is read out. Image data recognized as white in the readout image data is extracted in accordance with a predetermined algorithm, and a white balance (WB) coefficient is decided (this processing will be called WB calculation hereinafter). Chrominance signals are multiplied by the WB coefficient obtained as a result of calculation, thereby correcting white data.
When an image sensing element of frame read scheme in which image data is read by interlaced scanning on every other line is used, RAW image data of one frame is generated by two fields. If the color filters of the image sensing element have a Bayer matrix as shown in FIG. 7, only R and G signals are obtained by reading one field. That is, all pieces of color information cannot be obtained. For white balance calculation, at least R and B signals are necessary. In some cases, the WB calculation algorithm requires a luminance signal generated using all the R, G, and B signals. That is, when an image sensing element of frame read scheme in which image data is read by interlaced scanning on every other line is used, WB calculation is started after RAW data of two fields, i.e., one frame is written in the memory. For this reason, for the WB calculation, a time must be taken into consideration. This impedes the time between image sensing frames from shortening in, e.g., continuously photographing still images.